The invention more particularly applies to an <<open rotor>> turbine engine, i.e. comprising an unducted fan.
Such a turbine engine, more particularly known from the patent application FR 2 940 247, conventionally comprises a high pressure body comprising a high pressure compressor and a high pressure turbine rotationally coupled by means of a first shaft and an additional body comprising a low pressure compressor and an intermediate pressure turbine rotationally coupled by means of a second shaft.
The turbine engine further comprises a free power turbine, forming a low pressure turbine and comprising a first rotor (or internal rotor) and a second rotor (or external rotor). The turbine engine also comprises a system of contra-rotating impellers, i.e. respectively a first impeller and a second impeller driven by the low pressure turbine via an epicyclic speed reduction gear. The impeller system also comprises a stator.
The epicyclic speed reduction gear more particularly comprises a planet gear rotating about an axis, meshing with planets about axes belonging to a planet carrier, with the planets meshing with a radially toothed external crown gear, itself supported by a crown gear shaft. The shaft of the crown gear is rotationally coupled with the second rotor. Besides, the shaft of the planet gear is rotationally coupled with the first rotor.
Additionally, the shaft of the planet carrier is rotationally coupled with the first impeller and the shaft of the crown gear is rotationally coupled with the second impeller.
The turbine engine comprises an oil system lubricating and cooling the epicyclic speed reduction gear and the bearings supporting the rotating parts. Such system comprises an oil intake pipe provided with a pump for supplying oil and if need be control means located downstream from the supply pump, a supply pipe intended for supplying oil to a member to be lubricated and a recirculation pipe connected upstream from the supply pump, with the control means making it possible to direct all or part of the flow of oil from the intake pipe towards the supply pipe and/or towards the recirculation pipe. The fixed-displacement pump is driven into rotation by a mobile member of an accessory gear box positioned close thereto, via a power shaft.
Considering the footprint constraints, connecting a power shaft (i.e. a shaft making it possible to transmit a relatively high torque, for instance ranging from 90 to 900 N.m) with a mobile member of the epicyclic speed reduction gear is relatively complicated. Now, driving into rotation such oil supply pump cannot be obtained but with a power shaft.
It is reminded that an accessory gear box, or A.G.B. comprises a box containing a certain number of gears connected to devices or accessories, such as, for instance an electric generator, a starter, an alternator, hydraulic fuel or oil pumps, etc. . . . To drive such various gears, the power of the turbine engine is partially taken off at the high pressure body through a power take-off shaft. The speed of rotation of the various mobile members of the accessory gear box directly depends on the speed of rotation of the high pressure body of the turbine engine.
On the contrary, the speed of rotation of the various mobile members of the epicyclic speed reduction gear is not directly dependent on the speed of rotation of the high pressure body, but is directly dependent on the speed of rotation of the rotors of the low pressure turbine. The oil requirements of the speed reduction gear are thus uncoupled from the speed of rotation of the high pressure body. The oil system, and more particularly the pump, has a capacity covering the maximum oil rate required, and thus supercharges the epicyclic speed reduction gear with oil out of the operation point for which the capacity of the pump has been designed. Such supercharging is combined with a limited capacity of discharging oil because of the speed reduction gear, more particularly at low rotation speed (oil discharge by centrifugal effect). The risk of flooding the speed reduction gear exists, which affects the operation, the performances and the service life thereof, generates heating and creates unbalance.